1. Field of the Invention
The present invention generally relates to power distribution systems and, more particularly to power distribution systems for distribution of power less than approximately 1000 feet from the power source connection and having reduced hardware requirements while exhibiting enhanced power conservation.
2. Description of the Prior Art
The use of electrical power has become substantially ubiquitous in most aspects of modern life. Accordingly, power distribution systems at many levels such as regions of a national or continental power grid, large industrial plants, building complexes, individual buildings such as offices, hospitals, apartments, homes and the like or even vehicles such as ships or aircraft are familiar and, until fairly recently, designs have been well-optimized to provide power in virtually all applications where power is needed. Such power distribution systems generally operate at standardized voltages of 110 or 220 volts except where distances that are involved require higher voltages, often at thousands of volts, so that currents and wire sizes required to carry them can be reduced and/or to reduce the resistive losses and consequent voltage drops over long wire lengths. In such systems, use of alternating current allows alteration of voltages to desired levels by the use of transformers and low frequencies (e.g. 50-60 Hz or sometimes 400 Hz where smaller and/or lower weight transformers are mandated) are favored for simplicity and reliability.
However, much of the efficiency and effectiveness of such systems is based on designs which assume that power demands will fluctuate only slowly at levels approximating an average demand or load with only limited capacity to handle peak loads. Arrangements to provide supplemental power for peak loads generally require some sort of stand-by switching arrangement for diversion of power from other loads or where excess power generation capacity is available. Such stand-by arrangements are often complex and cannot be brought on-line quickly while consuming some amount of power which may be significant. Such arrangements are also particularly problematic in power distribution systems for vehicles such as aircraft or ships or some special purpose land-based vehicles such as mobile health care or medical screening vehicles or in installations such as health care facilities having sporadically used high-load equipment where the ability to satisfy a peak load may be of high importance if not critical and sources of additional power are likely to be limited (e.g. separately powered generators which cannot be started quickly or which consume considerable fuel in a stand-by state). Further, in vehicles where external potential sources of excess power generation capacity are not available, there may be the additional criticality of space or weight limitations that, as a practical matter, may preclude power distribution in a conventional manner to answer peak power demands.
For example, a ship or aircraft of current design will often have a plurality of computers included in the design and may include equipment that may include additional computers and other apparatus which potentially have large power requirements or where full operational loads may be many times that of the average or stand-by operational modes (which may, in turn, be many times the load in a so-called “sleep” mode that can be returned to a stand-by or full operational mode very quickly). Such computers will generally require power at a plurality of different voltages (which may be generated internally from a single voltage input although each conversion carries its own level of inefficiency as well as increasing the size and weight of each of such computers and equipment). Where space and weight are critical and power is required at different voltages, it has been proposed to provide power distribution at such a plurality of voltages or at least a plurality of voltages from which the required voltages may be developed. However, the disparity between peak power requirements and stand-by or sleep state power requirements of computers are becoming greater and the gain in space and weight savings is becoming increasingly limited, especially at the load location, due to the need to supply transient power requirements from power conversion devices within limited weight and volume specifications, particularly if the power is supplied from low frequency alternating current due, in part, to stringent regulation requirements.
The gains possible from such an approach are further reduced as the number of voltages required to be distributed is increased. That is, while the number of voltages required by any particular computer or individual piece of equipment may be less than ten, the number of different voltages required over all of the computers and equipment and their foreseeable replacements and upgrades may be significantly larger. Moreover, the power distribution system, as originally constructed, would generally provide all of the needed voltages that can be anticipated over the useful lifetime of the power distribution system whereas the computers and other equipment may be replaced or upgraded many times during such a period and such replacement computers or equipment may require different voltages than the computers or equipment they replace. For instance, the useful lifetime of an aircraft or ship may be (or may be extended to be) in excess of fifty years while the period of obsolescence of computers included therein may be three to ten years.
Moreover, it is becoming increasingly common to build ships and aircraft which can satisfy many different purposes and functions through interchange of equipment which may have distinctly different voltage requirements. Thus, if power distribution must be provided at low voltage and high current, the space available for the necessary power cables alone can easily be exceeded by large cables carrying even a relatively small number (e.g. 10-12) of different voltages. Similarly, deriving different low voltages locally to numbers of loads commonly encountered in vehicles or facilities at the present time can easily require a greater weight and/or volume of transformers than can be provided.
Accordingly, conventional power distribution system designs are being found to be inadequate, substantially less than optimal or simply not feasible increasingly often. For example, while a power distribution system of maximum tolerable size and weight for a given application might well accommodate loads well above average loads, the maximum power that can be delivered may be only a relatively small fraction of the potential peak load possible if potential loads are to be concurrently supplied with adequate power while diversion of power from other systems is much less likely to be possible in a vehicle. Moreover, additional power generation and distribution apparatus of conventional design that might be tolerable to accommodate peak load carry the additional cost of consuming stand-by power or may be brought on line only slowly, which may be deemed inadequate and an unacceptable operational constraint, particularly in vehicles. Thus, it is seen that conventional power distribution architectures are inadequate for many modern applications.